Can the science of happiness be trusted?

Partly, and its own researchers are still arguing about how much. Positive psychology, the scientific study of what contributes to well-being and flourishing, has some real evidence: a meta-analysis of 49 studies found that its exercises, such as writing gratitude letters, improved well-being and lowered depression. But a later meta-analysis that used only higher-quality studies, 39 of them with 6,139 participants, found effects that were still positive months later, yet weaker. And critics have gone as far as calling the field a pseudoscience with poor replication.

It was launched in 1998, when the psychologist Martin Seligman made it the theme of his year as president of the American Psychological Association, pushing back against a discipline that had mostly focused on mental illness.

Seligman was an unlikely messenger. He first became known for the theory of learned helplessness, built on experiments in the 1960s where dogs conditioned with electric shocks stopped trying to escape even when escape became possible. Later he turned toward the opposite question, and wrote a string of books, from Learned Optimism to Flourish. In Flourish he offered a five-part summary of well-being, PERMA: positive emotions, engagement, relationships, meaning, and accomplishment.

The field has also drawn serious criticism. Critics point to weak theorizing and shaky measurement, and argue it fails to credit decades of earlier research on what makes people function well. Researchers have also studied a side effect called positive illusions, unrealistically rosy self-views once thought to protect people from negative feedback, which later research linked to poorer relationships and negative workplace outcomes. One critic, Barbara Held, points to the movement's own inconsistency about how much room negativity deserves in a good life.

So positive psychology sits in an odd spot: a field built to study flourishing scientifically, whose own scientific standing is still being argued over.